The present invention relates to the field of transmission and reception of multiple signals using multiple transmission antennae and multiple receivers. More particularly, the invention relates to the use of multiple transmission antennae for the purpose of improving the quality of digital data communication. Recently, the use of digital communications using multiple input-multiple output (MIMO) antenna arrays has been successfully used for enhancing the transmission and reception capacity of signals. Compared with a single-input single-output (SISO) system, a MIMO system can improve this capacity by a factor of the total number of antennas.
Prior art techniques for decoding MIMO antenna arrays include the BLAST method, linear equalization, space-time coding, spatial modulation and maximum likelihood. The most notable recent use was in the BLAST (Bell-Labs Layered Space-Time) system which provides a method of decoding signals based on their received strength. The stronger signals are located and decoded. The strongest signal located by the system is then subtracted out and the next strongest signal located is decoded. This process is continued until the different signals are successively located in a layered approach. This method involves complex signal processing for determining the strongest signal. Linear equalization includes calculating a pseudo-inverse matrix for the channel matrix. Space-time coding can be used in multiple-input systems in order to reduce the power level required for data transmission at a particular data rate, while maintaining a certain error rate. Similarly, space-time coding can be used to obtain a low error rate, while maintaining a particular data rate and power level. The Spatial processing modulation method is based on multiple antenna arrays. Said modulation method improves the communication efficiency of wireless systems by decreasing the bit error rate and increasing the data rate. The maximum likelihood method includes searching all possible combinations of the received data in order to determine the sequence that is most likely to have been transmitted based on information from the received signal vector and the additive noise. However, increasing the number of antennae makes the maximum likelihood method computationally infeasible and substantially degrades the performance of linear equalization and BLAST.
Numerous attempts for reducing the computational complexity of signal processing inherent in digital data communication have been made in recent years. For example, U.S. Pat. No. 6,377,631, proposes a system which operates with an orthogonalizing signal procedure including a plurality of transmitter antenna elements, which decomposes the time domain space-time communication channel that may have inter symbol interference (ISI) into a set of parallel bins, wherein said ISI is reduced.
Another attempt to reduce the complexity of digital data communication is made in U.S. Patent Application No. 20030161258, which proposes a reduced computational complexity for the MIMO communication system, said system including a joint encoding and decoding scheme. Due to the performance of these joint operations, the calculations required increase only linearly and not exponentially according to the number of transmittal antennae.
However, none of the existing MIMO methodologies propose an improved reduced complexity maximum likelihood decoder for receiving and decoding simultaneously a plurality of transmitted signals.
It is thus an object of the invention to provide a reduced complexity MIMO decoder for receiving and decoding simultaneously a plurality of transmitted signals, wherein said computationally efficient decoder is accomplished by alleviating the computational complexity of optimal MLE methods while maintaining most of the performance gain.